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drm/i915: Reduce locking around i915_active_acquire_preallocate_barrier()

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As the conversion between idle-barrier and full i915_active_fence is
already serialised by explicit memory barriers, we can reduce the
spinlock in i915_active_acquire_preallocate_barrier() for finding an
idle-barrier to reuse to an RCU read lock to ensure the fence remains
valid, only taking the spinlock for the update of the rbtree itself.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Thomas Hellström <thomas.hellstrom@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200731085015.32368-6-chris@chris-wilson.co.uk
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
This commit is contained in:
Chris Wilson 2020-07-31 09:50:14 +01:00 committed by Joonas Lahtinen
parent e28860ae21
commit 9ff33bbcda
1 changed files with 5 additions and 5 deletions
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10
drivers/gpu/drm/i915/i915_active.c
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@ -807,7 +807,6 @@ static struct active_node *reuse_idle_barrier(struct i915_active *ref, u64 idx)
if (RB_EMPTY_ROOT(&ref->tree))
return NULL;
spin_lock_irq(&ref->tree_lock);
GEM_BUG_ON(i915_active_is_idle(ref));
/*
@ -833,9 +832,9 @@ static struct active_node *reuse_idle_barrier(struct i915_active *ref, u64 idx)
prev = p;
if (node->timeline < idx)
p = p->rb_right;
p = READ_ONCE(p->rb_right);
else
p = p->rb_left;
p = READ_ONCE(p->rb_left);
}
/*
@ -872,11 +871,10 @@ static struct active_node *reuse_idle_barrier(struct i915_active *ref, u64 idx)
goto match;
}
spin_unlock_irq(&ref->tree_lock);
return NULL;
match:
spin_lock_irq(&ref->tree_lock);
rb_erase(p, &ref->tree); /* Hide from waits and sibling allocations */
if (p == &ref->cache->node)
WRITE_ONCE(ref->cache, NULL);
@ -910,7 +908,9 @@ int i915_active_acquire_preallocate_barrier(struct i915_active *ref,
struct llist_node *prev = first;
struct active_node *node;
rcu_read_lock();
node = reuse_idle_barrier(ref, idx);
rcu_read_unlock();
if (!node) {
node = kmem_cache_alloc(global.slab_cache, GFP_KERNEL);
if (!node)